EPDM seal

EPDM is the water and steam elastomer. ERIKS lists its strengths as resistance to heat, water and steam, alkali, mild acidic and oxygenated solvents, ozone and sunlight, and adds that EPDM compounds withstand brake fluids and Skydrol and other phosphate ester-based hydraulic fluids.

The gap is a single, large one. ERIKS does not recommend EPDM for petrol, petroleum oil and grease, or hydrocarbon environments, and states that the peroxide-cured grades are not resistant to mineral oils, greases and fuels. Trelleborg Sealing Solutions puts it the same way: EPDM is not recommended for a system designed to hold a petroleum-based product, because it swells excessively.

That gap is the reason the elastomer question exists at all. Each polymer has its own chemical window and the windows do not line up. FKM, sold as Viton, covers the hydrocarbons EPDM cannot and struggles with things EPDM shrugs off. PTFE covers the widest range of all and gives up resilience for it. Check every elastomer in the pump against your medium on its own, because none of them are covered by the casing material's rating.

An EPDM seal fails in mineral oil by swelling, not by cracking. The ring takes up the oil, grows, loses hardness and stops generating the contact force it was designed around. By the time it leaks it looks soft and oversized rather than damaged, which is why the diagnosis often lands on the pump instead of the seal.

The trap is that this includes the grease it was fitted with. A mineral-oil based assembly grease is attacking an EPDM O-ring before the pump has run a minute. Use a lubricant the seal manufacturer states is compatible.

The same rule bites on the food side, where it is easy to miss. A hygienic duty carrying fats or edible oils is not an EPDM duty, and it is what the FPM option on Alfa Laval's hygienic ranges is there for.

EPDM is the standard elastomer on hygienic and potable pumps because a cleaning cycle is hot caustic, and hot caustic is what EPDM is good at. A clean-in-place routine puts alkaline detergent through the pump at temperature, on a schedule, for the life of the plant. An elastomer that softens in it is not a candidate whatever it does with the product.

The manufacturers' own specifications show where that lands:

• Alfa Laval quotes EPDM as the standard product-wetted elastomer on the DuraCirc, OptiLobe, SolidC and SX alike, and offers FPM against the duties EPDM will not take.
• Alfa Laval LKH UltraPure is quoted at -10°C to +140°C with EPDM elastomers, and its EPDM is declared to USP Class VI, 121°C, Chapter 87 and Chapter 88.
• Ebara builds the 3M in an E version with EPDM elastomers and a carbon, ceramic and EPDM shaft seal, and it is that version which holds WRAS approval 2206044. A different elastomer on the same hydraulics is a different product to the scheme, which is why we ask what the medium is before quoting the 3M.

So on a potable or hygienic duty the elastomer is not a detail you settle at the end. It is what the certificate is written against.

On most pumps the elastomer sets the temperature window, not the casing or the hydraulics. Look at any shaft seal table and the same pump is quoted over a different range depending on which elastomer is in it. Grundfos publishes the CR cartridge seal options that way. The HQQE seal, silicon carbide against silicon carbide on EPDM, is rated -40°C to +120°C. The HQQV seal, identical faces on FKM, is rated -20°C to +90°C. Same pump, same faces, and EPDM has the wider window at both ends.

Ebara's 3M shows the same thing. The standard build on NBR stops at +90°C; the E build on carbon, ceramic and EPDM runs -20°C to +120°C.

Read the small print under the Grundfos table before you lean on any of those numbers. Grundfos states the standard seal range for clean water and water with anti-freeze. It is a rating for a clean duty, not a promise about whatever is actually in your line. Tell us what is in the liquid before the seal gets picked.

EPDM is the wrong choice in three cases, and the first is the common one.

Anything oil-based. Fuels, mineral oils, greases and hydrocarbon solvents all swell it. That is an FKM duty, or a PTFE one if the medium is aggressive as well as oily.

Media outside both windows. Strong oxidisers, hot concentrated acids and chemically active organic compounds are where the specification moves away from moulded elastomers altogether, towards a PTFE bellows or a seal-less build. The reasoning behind that step sits on our corrosive duty page.

A compliance claim you cannot evidence. "EPDM" on a datasheet is a polymer family, not an approval. A WRAS Material Approval covers one non-metallic component, tested as a compound, and a USP Class VI declaration covers the specific elastomer a manufacturer names. Neither transfers to a different EPDM compound from a different supplier. Ask which compound, and ask for the certificate that names it.

The medium, its concentration and its temperature, and whether the pump gets cleaned in place and with what. That last question is the one that separates a hygienic enquiry from a general one, and it is nearly always missing.

Treat any chemical resistance chart you have been handed with some caution. Trelleborg Sealing Solutions notes that most such charts report room-temperature exposure and that chemical attack is time-dependent, so a material that holds for an hour at ambient can fail on a continuous hot duty. We will check your medium against the manufacturer's data for the actual build. Where the choice is genuinely difficult, the seal manufacturer's advice is the one to take, and we will go and get it.